Several varieties of kale are among the USDA certified organic vegetables that Andrew and Melissa Dunham grow on their farm in Grinnell, Iowa. (Amy Mayer/Harvest Public Media)

On a wet, grey day in Grinnell, Iowa, the rain beats a rhythm on the metal roof of a packing shed at Grinnell Heritage Farm. Crew member Whitney Brewer picks big bunches of kale out of a washing tank, lets them drip on a drying table and then packs them into cardboard boxes.

Like most farms in the United States, this one uses ample labor, harvesting tools and technology, and readily available refrigeration to ensure that most of its produce makes it to market. Most food that can’t be sold is eaten by the crew or donated to area food banks that can distribute it to people who need it.

Andrew Dunham, who is the fifth generation of his family to farm this land, says what little edible material accumulates that doesn’t get off the farm, is put back into the soil as part of a compost pile.

Just outside the shed where the kale is being packed, a 15-bushel crate collects waste material for compost. It’s less than half full on a recent day. Dunham looks down into it at the leaves, stems, paper and small melons destined for the compost pile.

“We had some vines that died in the field, so we don’t want to market those in case they don’t taste very good,” he said. “But the crew likes to eat a lot of melons and I think they’ve had their fill. So we just composted the ones they didn’t want to take home. And then you see some sunburnt potatoes, nobody wants those.”

There are a few rotten eggplants and some bad carrots, too. Weather damage, funny shapes and odd sizes all can make a fruit or vegetable hard to sell. In all, 20 percent of produce grown on U.S. farms never makes it to consumers, according to estimates by the Natural Resources Defense Council, an environmental group.

Dunham says occasionally edible food gets left in the field, which is referred to as “walk-bys,” because the farmer walks by and just doesn’t bother harvesting.

“Like in a beet field, you might have a number of beets that are golf-ball size that would be perfectly fine for pickling,” Dunham said, “but there’s no way that we’re going to send a crew out to pull golf-ball size beets all day and get 300 pounds of golf-ball size beets that nobody wants to buy.”

He says tilling those beets under will bring more value to the operation than trying to harvest and market them, thanks to the nutrients they return to the soil. Food safety scares, a lack of affordable farm labor and weather issues sometimes force farmers not to harvest portions of their crop, though “walk-bys” account for relatively little waste.

To be sure, we waste a lot of food in this country. The Environmental Protection Agency estimates that we threw away about 36 million tons of food in 2012. But most of that loss happens after it leaves the farm.

Dunham’s wife and business partner, Melissa Dunham, says after sales, donations, and workers taking their fill, not much gets wasted on this farm.

“I would say we probably compost less than 1 percent of edible food that could either be donated or consumed,” she said.

The situation looks very different in many other regions of the world.

“In developing countries, most of the waste is at the production level. I would say it’s a big number, it’s anywhere from 25-30 percent,” said Ajay Nair, a professor of horticulture at Iowa State University. “And the reason is the lack of infrastructure to move that produce quickly.”

Roads are in bad shape, or practically nonexistent, in places. There aren’t enough refrigerated trucks or they are unreliable. Plus, Nair says, farmers in poor countries may have fewer tools available to prevent on-farm waste.

“They may not be well versed in how to manage a pest or disease and if it comes to a field, the produce is lost,” Nair said.

A United Nations Report found that in developing countries, more than 40 percent of food waste happens on the farm or in the processing part of the food chain. In contrast, in industrialized countries, more than 40 percent of food waste happens at the retail or consumer level.

“Food waste at consumer level in industrialized countries (222 million ton) is almost as high as the total net food production in sub-Saharan Africa (230 million ton),” the UN Food and Agriculture Organization reports in its 2011 study “Global Food Losses and Food Waste.”

While most produce is highly perishable, grains such as corn, wheat and soybeans are less vulnerable. Here in the Midwest, on-farm grain loss is barely two percent. But in certain African and Asian countries, farmers lose up to 10 percent of their grain. Dirk Maier, co-director of the Innovation Lab for the Reduction of Post-Harvest Loss at Kansas State University, says he’s confident some of what makes farming so efficient here can be exported to farmers abroad.

“The challenge is, how do you help within the right cultural context and societal context and also economic context to help them adopt technologies that you know will help them?” Maier said.

Take grain storage for instance. It has been a game-changer in parts of the U.S. Corn Belt. Maier says it could help small farmers who want to keep some grain safely on their farms, perhaps to feed a goat or some chickens. But if they are still drying corn on the cob and shelling it by hand, the type of grain bins that work so well here will not be the right next step.

Still, Maier says, to meet the food demands of a growing global population, farmers in the developing world have to cut the amount of food left in the field and lost in transit.

“If we can reduce those,” he said, “that is a major contribution to the food production system because it takes away the pressure of how much food has to be grown on that many more acres in order to make up for that post-harvest loss.”

If less food is lost on the farm, more people can be eating. And farmers everywhere will be helping curb hunger in their own backyards.